Evaporant source



p 6, 1966 s. c. ROBERTS, JR, ETAL 3,271,562

EVAPORANT SOURCE 2 Sheets-Sheet 1 Filed June 30, 1964 MOEDOW Ev mw.

mOmzww JOmPZOU Am WW INVENTORS GILBERT C. ROBERTS JR.

GIORGIO G.VIA BY W A ATTORNEY Se t. 6, 1966 c, ROBERTS, JR, ET AL3,271,562

EVAPORANT SOURCE 2 Sheets-Sheet 2 Filed June 30, 1964 FIG. 2

FIG.3

United States Patent 3,271,562 EVAPORANT SOURCE Gilbert C. Roberts, Jr.,Owego, N.Y., and Giorgio G. Via,

Rockvilie, Md., assignors to International Business MachinesCorporation, New York, N.Y., a corporation of New York Filed June 30,1964, Ser. No. 379,307 8 Claims. (Cl. 219-275) This invention relates toapparatus for carrying out material deposition processes, and moreparticularly to an improved, high capacity evaporant source for vacuumdeposition equipment.

Considerable interest has developed in recent years in the use of vacuumdeposition techniques in the manufacture of electronic circuitries andthe like. Early equipments employed technology similar to that found inthe art of optical goods manufacture and even equipments especiallydesigned for the particular requirements of electronic circuitryfabrication were generally of the small experimental, bell jar variety.These equipments have not been, in general, suitable for depositingrelatively thick films, such as employed in insulation in vacuumdeposited electronic circuitry, on an economical, mass basis.

Accordingly, there has existed a need for improved high capacityevaporant sources particularly suited to quantity production of vacuumdeposited electronic circuitries. At the same time, it is desired topreserve the control and perfection of result which are among thefactors which lead the circuit designer to employ vacuum depositiontechniques in the first place. Thus, the evaporant source should becapable of use in the production of films which are reliably pinholefree and particle free, the deposition rate should be accuratelycontrollable, and other parameters such as stray radiation must beadequately controlled.

In accordance with the present invention, an improved high capacitysource for an evaporant such as silicon monoxide is provided. In oneconfiguration, it has a wide range of deposition rates controllablebetween zero and eight hundred angstroms per second and has a siliconmonoxide charge capacity of one million angstroms, thus fitting it wellto quantity production of fairly thick, for example ten thousandangstroms, silicon monoxide insulator films in electronic circuitries.These characteristics are achieved by a combination including a finnedor a convoluted heater providing efficient heat transfer to a largecharge of silicon monoxide while preserving close control over theentire evaporant mass. A separately heated baffle arrangement operatesto prevent particle ejection from the evaporant mass and also tends tostandardize the infrared radiation from the face of the evaporant mass.At the same time, cooling means are provided for the other portions ofthe apparatus such as the electrical connections and the housing so thatstray radiation is minimized and high temperature operation of theevaporant mass itself is feasible.

Accordingly, an object of the present invention is to provide animproved high rate, high capacity evaporant source for use in vacuumdeposition systems.

Another object of the invention is to provide an evaporant source asaforedescribed which is accurately controllable over a wide range ofevaporation rates.

Still another object of the invention is to provide, in

an improved evaporant source as aforesaid, effective, high capacitybaflle means for preventing particle ejection from the evaporant mass.

Still another object of the invention is to provide an improved widerange, high capacity evaporant source apparatus as aforesaid, in whichexcess radiation of infrared energy is avoided.

Yet another object of the invention is to provide an improved high rate,high capacity evaporant source as aforedescribed which is easilyreloadable, and is economically reconditionable, thus facilitatingemployment in high volume usage.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of a preferred embodiment of the invention, as illustratedin the accompanying drawings.

FIG. 1 is an elevation view, partly broken away, of an evaporant sourceapparatus in accordance with a preferred embodiment of the invention;

FIG. 2 is a fragmentary top plan view, turned counterclockwise, of theapparatus of FIG. 1;

FIG. 3 is a sectional view taken about along line 3-3 of FIG. 2; and

FIG. 4 is an electrical and coolant flow diagram applicable to theapparatus of FIG. 1.

Referring more particularly to FIG. 1, a preferred embodiment ofapparatus in accordance with the invention may be mounted by adeposition source chamber door 10 in a large, production type,multi-statiou, evaporator apparatus, indicated fragmentarily at 12. Thedoor mount of the apparatus provides for convenient servicing andreplacement of the same and facilitates feedthrough of the electricaland cooling connections to the evaporant source of the invention withoutneed of detachable couplings within the vacuum chamber of the apparatus.Accordingly, the door 10 carries a pair of brackets 14 which mount theevaporant source 16 itself and also is provided with feedthroughs fortwo electrical and three fluid coolant circuits as will be described ingreater detail hereinafter.

As shown more clearly in FIGS. 2 and 3, the evaporant source vessel 16comprises an outer box 18 which may be of copper or other suitablethermally and electrically conductive material, having a lining 20 ofelectrically insulative refractory material such as magnesium silicate.Mounted within the liner 20 is a convoluted heating element 22 ofsuitable electrical resistance material such as tantalum, theconvolutions of which form a number of fin-like configurations providinga plurality of pockets 24 for receiving a large charge of evaporantmaterial, such as silicon monoxide. The heating element 22 is formedwith flanges 26 to give it rigidity, and spacer means such as ribs 28formed in the sides of the liner 20 and keying with the spaces 30between the convolutions of the heating element provide mechanicalsupport for the same.

Electrical connections to the heating element 26 are made by a bus 32,of copper or other suitable material, cantalevered from the door by oneof the feedthrough connections, and by a flange fitting 33 on theconductive source vessel box. Referring again to FIG. 1 in conjunctionwith FIG. 2, the bus 32 is one of a pair including another bus 34, whichsupplies power to a bafile heater described more fully hereinafter. InFIG. 1 the charge heater supply bus 32 is largely hidden by otherportions of the apparatus. It is substantially identical in constructionto the bus bar 34 which is seen clearly in that figure, and accordinglya single description will suffice for both.

Referring then to the construction of bus bar 34, the bus bar iscantalever mounted by a feedthrough fitting 36 secured by a nut 38 in anaperture 40 in the door and insulated therefrom by material 42. Thefitting 36 is of copper or other suitable electrically conductivematerial so as to provide a good electrical path from the bus 34 to aconnection ear 44 mounted by the fitting 36, as by a nut 46. The fitting36 is bored as indicated at 48 to provide cooling water feedthrough toand from a loop of tubing 50 of copper or other suitable materialbraised or otherwise secured to the underside of the bus 34 so as tocool the same. Electrically insulating couplings such as indicated at 52are provided for electrical isolation of this cooling conduit from therest of the cooling system, as will be described hereinafter.

As shown most clearly in FIG. 3 the charge heater supply bus bar 32,cooled by a conduit 54 similarly to the bus bar 34, clamps, by a plate56 and fasteners 58, one end portion 60 of the heater 22. Thus, thisheater connection tab portion 60 is in electrical communication with theconnection ear of the bus 32. Ground connection is made at the other endconnection portion 62 of the heater to the aforementioned groundconnection flange 33 borne by the source outer box 18. This groundconnection also serves for making connection to one terminal portion 66of the baffle heater 68 (hereinafter more fully described), by means ofclamp plates 70, 72 and fasteners 74. 1

Cooling means for the outer box 18 and the ground connection 64 areprovided in the form of copper or other suitably electrically andthermally conductive cooling coil 64 braised or otherwise attached tothe four sides and bottom of the copper box 18. This cooling coil 62makes a good ground connection to external circuitry by means of afeedthrough 68 which may be in all respects similar to the feedthrough36 above described, except that, since it is a ground connection it doesnot require insulation from the door 10.

The evaporant vessel is covered by a removable top portion constitutingan evaporant exit baffle device. In the illustrated embodiment, as seenmost clearly in FIGS. 2 and 3, the bafile comprises a metallic U-shapedframe 80 mounting a rectangular inner frame 82 of suitable insulatingmaterial such as magnesium silicate. The inner frame 82 is grooved toreceive the bafile heater 68 which is formed from a strip of tantalum orother suitable heater material folded upon itself to provide an upperdiaphragm 84 and a lower diaphragm 86. The upper diaphragm is perforatedto provide a first array of holes 88 and the lower diaphragm isperforated to provide a second array of holes 90, in offset relation tothe first array 88. Accordingly, the first and second arrays provide atortuous passageway through the baffle for evaporant vapors. To avoidthe possibility of mechanical ejection of large particles from thesource pockets 24 through this tortuous passage, it is preferred thatscreening such as 100 mesh tantalum screening 92 be provided, tackwelded to the lower diaphragm 86 so as to cover the holes 98 therein.

Spacer devices such as ceramic rods 92 are provided which maintain thediaphragms in spaced parallel relation for providing the desired pathfrom one array of holes 90 to the other array 92. The insulating frame82 may be made from several pieces held in assembled relation by a wireband or hoop 94 about the outside of that frame. This subassembly isremovable through the open end of the U-shaped outer frame 80, so thatthe battle is easily reconditionable. The baffle assembly is removable,for such reconditioning as well as for recharging and/or reconditioningthe evaporant heater assembly. Thus, in the illustrated construction,the baffie outer frame 88 is 4 mounted by angles 96, 98 attached bymachine screws 100 to flanges 102, 104 mounted by the box 18.

The ends of the heater strip 68 forming the baffle diaphragms 84, 86extend to provide connection portions whereby electrical current ispassed through the bafile strip or ribbon 68 to heat it for preventingaccumulation of evaporant deposits upon it. Electrical connection ismade to the bafiie for this purpose by the aforedescribed baffle heaterbus 34 cantilevered by its insulated throughfitting 36 in the vacuumchamber door 10, and by the aforementioned connection to the flange 33on the evaporant vessel box.

FIG. 4 shows in schematic form the separate electrical control of theevaporator heater and the baflie heater. It will be understood of coursethat the evaporant heater can be and usually is controlled by depositionrate or other suitable sensors not shown in FIGS.. l-3 but indicated inFIG. 4, as well as by other machine controls. FIG. 4 also showsschematically the coolant fiow system.

In the scheme illustrated in FIG. 4 the charge heater 22 and the baffieheater 68 are connected to a common ground in conformity with thearrangement of FIGS. 1-3. As aforedescribed, this ground return isthrough the body of the box 18 and the cooling conduit 64 for that part.This interconnection between the box 18 and the cooling conduit 64 .isindicated schematically at 110. The ground connection at the feedthrough68 of the conduit 64 to the external electrical system of the apparatusoutside the door 10 is indicated at 112. In contrast, the electricalisolation of the cooling conduits 50, 54 of the baffie heater bus 34 andthe charge heater 32 is indicated by the schematic representation ofinsulating couplings 52A, 52B, 52C and 52D exemplified in FIG. 1 by theshowing (at 52) of one of these insulators. As shown in the diagram ofFIG. 4, the cooling conduits 50, 54 and 64 are connected to be suppliedwith cooling water from a suitable source 114.

The bafiie heater bus bar 34 is connected via its connection car 44outside the door 10 for energization by the secondary winding of anisolating transformer 120, the primary of which is energized in acontrollable manner by an auto-transformer 122 connected to a suitablesource of AC. power 124. Similarly, the connection ear of thefeedthrough fitting for the bus bar 32 of the charge heater is connectedfor energization by an isolating transformer 126 which is also suppliedthrough an adjustable auto transformer 128. However, in the illustratedarrangement, there is interposed between the power supply 124 and theauto transformer 128 a suit-able control 126, which may comprise asaturable reactor having an input control 128 responsive to anevaporation rate sensor 130 which may be of the ion gage or othersuitable type, located for intercepting a sampling of the evaporantstream emanating through the baffle from the source apparatus of theinvention.

In one example, an evaporator in accordance with the invention had anevaporant vessel box with a liner having interior dimensionsapproximately 2 /8 x 3 x 3 inches, a source heater made of 3 miltantalum 2% inches wide and 37 /2 inches long folded to form six pocketseach x 2 /8 x 3 inches. The baffle frame had an interior opening of 2% x3 inches and a b-aflle heater made of 3 mil tantalum and having aboutforty-two 7 inch perforations in each of its diaphragms, with 100 meshtantalum screening spot welded to the top surface of the bottomdiaphragm. A 3.5 k.v.a. power supply was provided for the charge heaterand a 2.0 k.v.a. power supply for the baffle. This device yielded adeposition rate which was controllable between zero and eight hundredangstroms per second at source to deposition substrate distance of 12inches. It was designed for evaporation of silicon monoxide at atwenty-four inch source-tosubstrate distance and had a capacity of 264grams of SiO which yielded one million angstroms percharge.

Larger configurations, such as the eight pocket version shown in thedrawings yielded up to 800 A./sec. at twentyfour inchessource-to-substrate distance, and, using a granulated SiO charge, had acapacity of over 500 grams of SiO, yielding about one million angstromsdeposition per charge at that distance.

Typical operating temperatures, in either version, for the baflle andcharge heaters are about 1450 C. and 1380 C. respectively. The bafflespacer rods 92 may be of commercially available thermo-couple tubing ofa suitable ceramic material. The fold 132 of the baffle heater 68 may beapertured to receive the rods 92, as required.

The illustrated evaporant source is easily rechargable by opening thedoor and removing the bafiie-cover device of the evaporant vessel.Replacement of the tantalum charge heater is a simple matter, since itis fastened only at its electrical connections. Similarly, the baffleheater can be replaced with facility by dis-assembly of its frame.

Although the charge capacity is large, the entire charge mass is inclose association with the charge heater for efiicient and controlledevaporation at high rates. So also, the baffle has large capacity andyet each individual orifice of that part is small and well protectedagainst particle ejection.

Since means are provided for cooling the connection buses and theevaporant source box, the only substantial radiation of infrared energyfrom the evaporant source of the invention is by the baffle. Since thebaffle heater is separately controllable, the baffle can be maintainedat a substantially constant or otherwise predetermined tem peraturedespite changes in the operating temperature of the evaporant sourcecharge heater, whereby control of the vacuum deposition processparameters is facilitated.

While the invention has been particularly shown and described withreference to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention.

What is claimed is:

1. In a vacuum deposition apparatus, an evaporant source comprising anevaporant charge vessel,

said vessel comprising a box structure and an evaporant charge heatermounted by said box structure,

said heater comprising a vertically finned structure of resistance metalformed to provide a plurality of vertically opening pockets,

and means on said heater and on said box structure for maintaining thepocketed configuration of said heater,

and bafiie means disposed to intercept vapors emanating from saidvessel.

2. In a vacuum deposition apparatus, an evaporant source comprising abox and an insulating liner within said box,

an evaporant change heater mounted by said liner,

said heater comprising an elongate strip of resistance metal folded toform a plurality of vertically opening pockets,

means on said heater and on said lining for maintaining the pocketedconfiguration of said heater,

and baffle means disposed to intercept vapors emanating from said box.3. Apparatus in accordance with claim 2, wherein said baffle meanscomprises a cover for said box.

4. In a vacuum deposition apparatus, an evaporant source comprising anevaporant charge vessel, said vessel comprising a box structure and anevaporant charge heater mounted by said box structure,

said heater comprising a vertically finned structure of resistance metalformed to provide a plurality of vertically opening pockets,

and means on said heater and on said box structure for maintaining thepocketed configuration of said heater,

and baffle means located to intercept vapors from said box,

said baifie means comprising a strip of resistance metal folded uponitself and means for maintaining the folded portions of the same inspaced parallel relation,

said folded portions being perforated in an offset manner with respectto each other,

and electrical connections for said strip for energizing the same as aheater.

5. In a vacuum deposition apparatus, an evaporant source comprising abox of electrically and thermally conductive material,

an electrically insulating liner within said box,

an evaporant charge heater mounted by said liner,

said heater comprising an elongate strip of resistance metal folded toform a plurality of vertically opening pockets, means on said heater andon said lining for maintaining the pocketed configuration of saidheater,

and a cover for said box comprising a bafiled exit means comprising astrip member of resistance metal folded upon itself and a refractoryinsulative frame receiving said member and comprising means formaintaining the folded portions of the same in spaced parallel relation,

said folded portions being perforated in an offset manner with respectto each other to provide a tortuous exit path.

6. In a vacuum deposition apparatus, an evaporant source comprising abox of electrically and thermally conductive material,

an electrically insulating liner within said box,

an evaporant charge heater mounted by said liner,

said heater comprising an elongate strip of resistance metal folded toform a plurality of vertically opening pockets, means on said heater andon said lining for maintaining the pocketed configuration of saidheater,

a cover for said box comprising a bafiied exit means comprising a heatermember formed by a strip of resistance metal folded upon itself and arefractory insulative frame receiving said member and comprising meansfor maintaining the folded portions of the same in spaced parallelrelation,

said folded portions being perforated in an offset manner with respectto each other, and the lower of said portions being provided with a meshscreen,

separate circuit electrical connections for said charge heater and saidbaffle heater,

and separate coolant conduit means for said electrical connections, oneof said electrical connections comprising said box.

7. In a vacuum deposition apparatus, an evaporant source comprising abox of electrically and thermally conductive material,

an electrically insulating refractory liner within said box,

an evaporant charge heater mounted by said liner,

said heater comprising an elongate strip of sheet tantalum folded toform a plurality of vertically opening pockets, flange means on saidheater and rib means on said lining for maintaining the pocketedconfiguration of said heater,

a cover for said box comprising a bafiied exit means comprising a heatermember formed by a strip of sheet tantalum folded upon itself and arefractory in sulative frame receiving said member and comprisingrefractory spacer means for maintaining the folded portions of the samein spaced parallel relation,

said folded portions being perforated in an offset manner with respectto each other, and the lower of said portions being provided with atantalum mesh screen,

separate circuit electrical connections for said charge heater and saidbafile heater,

and separate coolant conduit means for said electrical connections, oneof said electrical connections comprising said box.

8. In a vacuum deposition apparatus, an evaporant source comprising anevaporant charge vessel,

said vessel comprising a box structure and an evaporant charge heatermounted by said box structure,

said heater comprising a finned structure of resistance metal arrangedin said box structure to provide a 4/1954 Thorington 118-49 X 9/1963Silva ll8--49.1 X

OTHER REFERENCES Weed, D. S.: Evaporation Boat for Silicon Monoxide, IBMTechnical Disclosure Bulletin, vol. 2, No. 3, pp. 27 and 28, October1959.

RICHARD M. WOOD, Primary Examiner.

plurality of pockets in said finned structure opening 15 L. ALBRITTONAssistant Examiner from said box structure,

1. IN A VACUUM DEPOSITION APPARATUS, AN EVAPORANT SOURCE COMPRISING ANEVAPORANT CHARGE VESSEL, SAID VESSEL COMPRISING A BOX STRUCTURE AND ANEVAPORANT CHARGE HEATER MOUNTED BY SAID BOX STRUCTURE, SAID HEATERCOMPRISING A VERTICALLY FINNED STRUCTURE OF RESISTANCE METAL FORMED TOPROVIDE A PLURALITY OF VERTICALLY OPENING POCKETS, AND MEANS ON SAIDHEATER AND ON SAID BOX STRUCTURE FOR MAINTAINING THE POCKETEDCONFIGURATION OF SAID HEATER,